Gerber review a MUST.

Sometime ago I did a design for a customer.  We were using a custom soft rubber keypad that we were procuring from China.  The keypad, which had carbon contacts, when pushed would create electrical input to the electronic hardware.  I had to develop a PCB library component to accommodate this.  The design was sort of complex and looked like a spoked type of wheel.  Like many others in the industry, I have developed a set of guidelines that have proven themselves over the years.  One of these governances I adhere to is to place solder mask and paste per a set design rule within the library component itself.  Then when I use the component, depending on the design, I may alter it as needed through design scopes using classes within the schematic and pcb.  

Now it just so happens that this particular customer came back to me recently for a product update.  It involved some minor changes but one of these required rotating one of the keypad entries.  I was having trouble getting it to rotate correctly and ended up deleting it from the schematic and pulling a new part in.  Seemed simple enough except I forgot that I had set a parameter in the schematic that when pushed to the PCB would remove the solder paste.  Had I not reviewed the gerber files I would have missed this.  It is not to say that the PCB tool didn’t show the error but paste and mask many times are taken for granted and overlooked.  As designers we get caught up looking at pours, clearances, via sizes, thermals, pinouts, land patterns, and the list goes on. Solder paste on that keypad entry would have potentially caused grief with respect to electrical contact.  

The gerber files are a great way to isolate each drawing layer and show exactly what the board house will see when they go to build the board.  Some PCB manufacturers have a team of engineers who review drawings prior to board building, however there is no guarantee even with that service that the PCB engineering staff would second guess the designer and contact them for clarification.  Over the years I have found that gerber files have flagged about 50% of the errors I have had in my PCB designs.  They work great especially when it comes to reviewing the less glamourous part of our job as PCB designers such as solder mask and paste issues, design notes, drill tables, via tenting on thermal pads, etc.  Design review of this level is a must and will help prevent board re-spins from becoming the norm instead of the exception.